The present invention relates to an abnormality detecting device for an evaporative fuel processing system for processing evaporative fuel generated in a fuel tank containing fuel to be supplied to an internal combustion engine.
An abnormality detecting device for determining an abnormality in an evaporative fuel processing system is known from Japanese Patent No. 2857656, for example. In this conventional abnormality detecting device, a negative pressure (a pressure lower than the atmospheric pressure) generated in an intake pipe of an internal combustion engine is introduced into the evaporative fuel processing system to reduce the pressure in the evaporative fuel processing system, and the abnormality in the evaporative fuel processing system is determined according to the pressure in this system after the above pressure reduction. The evaporative fuel processing system includes a fuel tank, a canister for temporarily storing evaporative fuel generated in the fuel tank, and a charging passage for connecting the fuel tank and the canister.
According to the above abnormality detecting device, a leak in the fuel tank or the canister can be detected. However, a failure such that the charging passage is clogged cannot be detected.
It is accordingly an object of the present invention to provide an abnormality detecting device for an evaporative fuel processing system which can detect the clogging failure of the charging passage for connecting the fuel tank and the canister.
In order to attain the above object, the present invention provides an abnormality detecting device for an evaporative fuel processing system. The evaporative fuel processing system includes a fuel tank (9), a canister (33) for trapping evaporative fuel generated in the fuel tank (9), a charging passage (31) for connecting the fuel tank (9) and the canister (33), an on-off valve (36) provided in the charging passage (31) for opening and closing the charging passage (31), and a pressure sensor (15) provided in the charging passage at a position between the on-off valve (36) and the fuel tank (9). The abnormality detecting device includes pressure reducing means and clogging determining means. The pressure reducing means reduces a pressure in the canister (33) to a pressure which is lower than the atmospheric pressure in the condition where the on-off valve (36) is open. The clogging determining means closes the on-off valve (36) at the time of completion of the pressure reduction by the pressure reducing means, and determines that the charging passage (31) is clogged between the pressure sensor (15) and the fuel tank (9), when the amount of change (PTANKxe2x88x92PTGROSLK) in the pressure detected by the pressure sensor is less than a predetermined change amount (DPT2WYOK) after closing the on-off valve.
With this configuration, the pressure in the canister is reduced to a pressure which is lower than the atmospheric pressure in the condition where the on-off valve provided in the charging passage is open, and the on-off valve is next closed at the time of completion of this pressure reduction. Further, when the amount of change in the pressure detected by the pressure sensor after closing the on-off valve is less than the predetermined change amount, it is determined that the charging passage is clogged between the pressure sensor and the fuel tank. If the charging passage is normal, the closing of the on-off valve results in an increase in the pressure detected by the pressure sensor, because the pressure in a portion of the charging passage between the on-off valve and the fuel tank and the pressure in the fuel tank are averaged. In contrast, if the charging passage is clogged between the pressure sensor and the fuel tank, the pressure detected by the pressure sensor is held at the reduced pressure also after closing the on-off valve. Accordingly, when the pressure change amount after closing the on-off valve is less than the predetermined change amount, it can be determined that the charging passage is clogged.
Preferably, the pressure reducing means completes the pressure reduction in a short time period (TSDEC2, e.g., 3-5 seconds) so that a pressure in the charging passage may be reduced to a predetermined pressure (PDEC2) which is lower than the atmospheric pressure.
If the pressure reduction is executed for a long period, the pressure in the fuel tank decreases, which reduces determination accuracy. Therefore, by completing the pressure reduction in a relatively short time period, the pressure decrease in the fuel tank is substantially prevented so that good determination accuracy can be obtained.
Preferably, the clogging determining means executes the determination of clogging of the charging passage (31) after confirming no occurrence of a failure that the on-off valve (36) remains open and does not close in spite of being supplied with a valve closing command signal.
Preferably, the clogging determining means determines that the charging passage (31) is clogged between the pressure sensor (15) and the fuel tank (9), when the condition where the amount (PTANKxe2x88x92PTGROSLK) of change in the pressure detected by the pressure sensor (15) is less than the predetermined change amount (DPT2WYOK), continues over a predetermined time period (TPTLKS) or more.
Preferably, the clogging determining means determines that the charging passage (31) is clogged between the pressure sensor (15) and the fuel tank (9), when the pressure (PTLK0) detected by the pressure sensor (15) after closing the on-off valve (36) is lower than a predetermined pressure (PT2WYOK) which is lower than the atmospheric pressure, and the amount (PTANKxe2x88x92PTGROSLK) of change in the pressure detected by the pressure sensor is less than the predetermined change amount (DPT2WYOK).